Almost all interior spaces include artificial lighting to ensure proper light levels for a work environment and/or desirable light levels in a home environment. Traditionally, artificial lights are manually turned on or off from a wall switch to control lighting levels. In some cases, lighting devices may be dimmed, usually in response to user activation of a relatively simple wall-mounted dimmer. Lighting devices have also been controlled in response to ambient light detectors that turn on a light only when ambient light is at or below a threshold (e.g. as the sun goes down) and in response to occupancy sensors (e.g. to turn on light when a room is occupied and to turn the light off when the room is no longer occupied for some period). Often traditional lighting devices are controlled individually or as relatively small groups at separate locations.
With the advent of modern electronics has come advancements, including advances in the types of light sources as well as advancements in networking and control capabilities of the lighting devices. For example, solid state sources have become a commercially viable alternative to traditional light sources such as incandescent and fluorescent lamps. By nature, solid state light sources such as light emitting diodes (LEDs) are easily controlled by electronic logic circuits or processors. Electronic controls have also been developed for other types of light sources. As increased processing capacity finds its way into the lighting devices, it becomes relatively easy to incorporate associated communications capabilities, e.g. to allow lighting devices to communicate with system control elements and/or with each other. In this way, advanced electronics in the lighting devices as well as the associated control elements have facilitated more sophisticated lighting control algorithms as well as increased networking of lighting devices.
In view of the power and environmental concerns, many installations do not rely solely on artificial lighting during daytime hours of operations. Daylighting is a practice of placing or constructing elements of a building to distribute daylight from outside the building into interior space(s) of the building, which may reduce the need for artificial lighting during daytime hours. Traditional examples of daylighting devices involved appropriate sizing and placement of windows in walls or doors of the building or of skylights or the like in roofs/ceilings of the building. More sophisticated daylighting equipment utilizes optical collectors, channels, reflectors and optical distributors to supply and distribute light from outside the building to regions of the interior space. Although various daylighting systems may, be adjustable, they typically are passive in nature. The light supplied to the interior region of the building is redirected (and/or produced in response to) sunlight from the exterior region of the building. Artificial lighting may be combined with daylighting equipment, either in the form of luminaires in the vicinity of a daylighting device or by incorporation of an artificial light source within the same structure that implements the daylighting device. The addition of artificial lighting to a daylighting system provides additional light to the interior region, e.g. in regions where the daylighting may not be adequate and/or for days or times when the collected sunlight may not be sufficient.
Some environments that maintain a relatively uniform lighting level using both daylighting devices and artificial lighting employ closed-loop control systems a that uses monitoring device to sense the light level in the room and a controller that control either or both of the artificial lighting or a light modulator coupled to the daylighting device. These systems increase or decrease the light levels of the artificial and/or daylighting light sources in response to changing levels of sensed light. It is difficult to determine the proper location for the sensors used by these systems as the sensor placement at one location may result in undesirable lighting at a different location.